@Aadhi: That sounds like your calibration might be wrong. Did you note that you have to enter the distance in 'mm' and the time step in 'ms' during calibration? If that doesn't fix your problem, you could send me some example images.
hi @ William
here after my analysis i got the u velocity is 0.00025 m/s, but when i did manually in channel i got around 0.205 m/s, in my analysis i used Canon EOS 7D camera is used. here i got the error as 1/1000, please give any one exact explanation.